Methods and systems for wireless networks relays

ABSTRACT

Methods and systems are provided for use with wireless networks having one or more cell in which each cell includes a base station (BS), at least one relay station (RS) and at least one mobile station (MS). The at least one relay station can be used as an intermediate station for providing communication between the BS and MS. Methods are provided for allocating OFDM resources for communicating between the BS, RS and/or MS for example dividing transmission resources into uplink and downlink transmissions and methods of inserting pilot symbols into 
     transmission resources used by the RS. In some embodiments on the invention, the methods are consistent and/or can be used in conjunction with existing standards such as 802.16e.

RELATED APPLICATIONS

This application is a divisional application of U.S. patent applicationSer. No. 12/300,522 filed on Nov. 12, 2008, which claims the benefit ofand is a National Phase Entry of International Application No.PCT/CA2007/000965 filed May 31, 2007, and claims the benefit of U.S.Provisional Patent Application Nos. 60/809,341 filed on May 31, 2006,60/822,960 filed on Aug. 21, 2006, 60/863,873 filed on Nov. 1, 2006 and60/870,417 filed on Dec. 18, 2006, which are all hereby incorporated byreference in their entirety.

FIELD OF THE INVENTION

The invention relates to the field of wireless communications, morespecifically to systems and methods for supporting Orthogonal FrequencyDivision Multiplexed (OFDM) communication using relays.

BACKGROUND OF THE INVENTION

Orthogonal frequency division multiplexing (OFDM) is a form ofmultiplexing that distributes data over a number of carriers that have avery precise spacing in the frequency domain. The precise spacing of thecarriers provides several benefits such as high spectral efficiency,resiliency to radio frequency interference and lower multi-pathdistortion. Due to its beneficial properties and superior performance inmulti-path fading wireless channels, OFDM has been identified as auseful technique in the area of high data-rate wireless communication,for example wireless metropolitan area networks (MAN). Wireless MAN arenetworks to be implemented over an air interface for fixed, portable,and mobile broadband access systems.

In some wireless networks, a mobile station (MS) in a given cell is onlyserved by its serving base station (BS).

One drawback of such wireless networks is that MSs near an edge of thegiven cell suffer performance loss due to interference from other cellsin cellular networks and propagation loss in non-cellular networks whichresults in limited data rates and gaps in coverage of the given cell.

While soft hand off can be used in cellular networks to improveperformance to some extent for MSs at the cell edge, the improvedperformance comes at the cost of additional system complexity and aspectrum efficiency penalty.

One way to improve the performance is to introduce a fixed or mobilerelay station (RS) into wireless networks. The use of an RS may providea) enhanced system capacity, b) enhanced data rate and cell coverage, c)reduced MS transmit power requirements and d) allow less expensive poweramplification.

SUMMARY OF THE INVENTION

According to an aspect of the invention, there is provided a method foruse in an OFDM communication system employing relay stations comprising:dividing communications into frames each comprising multiple OFDMsymbols; dividing the frames into first and second groups of frames, thefirst group of frames being used for communication between a basestation (BS) and first tier RSs one-hop away from the BS, and forcommunications between the BS and its respective mobile stations (MSs),the first group also being used for communication between RSs of a 2Nthtier and RSs of a 2N+1th tier, N>=1, the RSs of the 2Nth tier being 2Nhops away from the BS, and any MSs the RSs of the 2Nth tier arecommunicating with, and the second group of frames being used forcommunication between RSs of a 2N−1th tier and the RSs of a 2Nth tier,the RSs of the 2N−1th tier being 2N−1 hop(s) away from the BS, and anyMSs the RSs of the 2N−1th tier are communicating with.

In some embodiments, dividing the frames comprises dividing the framessuch that the first group is odd frames and the second group is evenframes.

In some embodiments, the method further comprises: the BS communicatingwith mobile stations during the second group of frames at a reducedtransmission power with respect to the transmission power used fortransmitting to the RSs.

In some embodiments, the method further comprises, after entry into anetwork, each relay station transmitting a preamble and frame controlheader (FCH) channel on every frame.

In some embodiments, the method further comprises: defining DL RS_Zonesfor downlink transmission from a base station or an RS to another RS andUL RS_Zones for uplink transmission from an RS to another RS, or from anRS to BS, with remaining resources available for communication with MSs.

In some embodiments, defining DL RS_Zones comprises defining a zone sizeand a DL RS Zone starting location within the frame in time-frequencyaccording to one of: a fixed size; a size that is slowly changed througha management media access control (MAC) message; a size that isdynamically changed and forecast by BS and DL transmitting RSssubsequent to the change.

In some embodiments, the method further comprises transmitting R-MAPinformation to indicate the resource assignments for the DL RS_Zoneand/or the UL RS_Zone.

In some embodiments, transmitting the RS-MAP includes transmitting oneor more of: resource location information, resource size information,and modulation and coding scheme (MCS) information.

In some embodiments, the location information is a fixed offset relativeto the beginning of a frame or a fixed offset relative to RS_Zone.

In some embodiments, the modulation and code information is provided byat least one of: slowly updating the MCS information based on worst linkbudgets among all attached RS; and multicasting the MCS information tothe corresponding RSs when needed.

In some embodiments, transmitting multiple RS-MAP, each RS-MAP for arespective one RS or multiple RSs with similar channel qualities.

According to an aspect of the invention, there is provided a method foruse in an OFDM communication system employing relay stations (RSs)comprising: assigning a distinct pseudo-random noise (PN) sequence toeach base station (BS) and each respective RS.

In some embodiments, assigning the distinct PN sequence to each relaystation comprises including assigned PN index, DL_PermBase, and PRBS_IDfields management messages.

In some embodiments, the method further comprises for purposes ofrouting, identifying each BS or RS by a BS identification (BS ID) in aMAC management message.

In some embodiments, identifying each RS comprises assigning each RS aBS ID in a management message.

In some embodiments, assigning a distinct PN sequence for a mobile relaystation (MRS) is statically defined even when there is a handoff.

In some embodiments, the method further comprises defining for mobilerelay stations a system reserved sub-set of PN indexes so as to avoidcollisions when a MRS moves across the network.

In some embodiments, the PN index is re-assigned during a handoff, andfurther comprising informing any attached MSs of the change and/orperforming re-synchronization.

In some embodiments, the method further comprises: performingsub-channelization using bins, wherein each bin is a band ofsub-carriers in an OFDM symbol.

In some embodiments, performing sub-channelization using bins isperformed in a manner consistent with 802.16e AMC sub-channelization.

In some embodiments, a bin is defined as a band of contiguoussub-carriers (G) in one OFDM symbol, with each bin including at leastone pilot sub-carrier.

In some embodiments, the at least one pilot sub-carrier is: for oneantenna located in the bin at a sub-carrier indexed with floor(G/2); fortwo antennas located in the bin at a first sub-carriers indexed withfloor(G/2) for a first antenna and a second sub-carrier indexed withfloor(G/2)+1 for a second antenna; and for four antennas located in thebin at a first sub-carrier indexed with floor(G/2) for a first antenna,a second sub-carrier indexed with floor(G/2)−1 for a second antenna, athird sub-carrier indexed with floor(G/2)+1 for a third antenna and afourth sub-carrier indexed with floor(G/2)+2 for a fourth antenna.

In some embodiments, performing sub-channelization comprises formingsub-channels from contiguous sets of one or more bins over one or moreconsecutive OFDM symbols.

In some embodiments, the method further comprises performing DL resourcemultiplexing between BS and RS, between RS and RS, between BS and MS andbetween RS and MS on an FDM (frequency division multiplexing) basis.

In some embodiments, the method further comprises for all availablesub-carriers used for pilot and data in an OFDM symbol; dividing thesub-carriers into a set of major groups; and dedicating a number of themajor groups of the set of major groups to BS and RS transmission and RSand RS transmission.

In some embodiments, dividing the sub-carriers into a set of majorgroups and dedicating a number of the major groups is done in a mannerconsistent with 802.16e.

In some embodiments, a sub-channel is defined so as to enlargesub-channel size, each sub-channel defined to consist of a set ofclusters that are not contiguous.

In some embodiments, the method further comprises performing UL resourcemultiplexing between RS and BS, between RS and RS, between MS and BS andbetween MS and RS using the UL RS_Zones.

In some embodiments, the method further comprises: performingsub-channelization using bins, wherein each bin is a band ofsub-carriers in an OFDM symbol.

In some embodiments, a first bin definition includes pilot symbols, anda second bin definition does not include pilot symbols, and acombination of the two bin definitions is used for a given sub-channel.

In some embodiments, the method further comprises: initially assuming anentire frame resource is initially available for use for RS relatedtransmission (DL/UL); defining RS sub-channels; assigning resources forMSs first; then assigning resources for RSs with RS sub-channels;resources assigned to RS that are already occupied by MSs are puncturedout from the assigned resource for RS.

According to an aspect of the invention, there is provided a methodcomprising: transmitting R-MAP information in at least one frame of aseries of frames, each frame comprising multiple OFDM symbols, toindicate configuration of a transmission resource and/or assignment of atransmission resource for downlink and uplink communication between abase station and at least one relay station one hop away from the basestation, or between a relay station and at least one other relay stationone hop away from the relay station.

In some embodiments, transmitting the R-MAP information comprises:transmitting an indication that the information is R-MAP information,transmitting a total number of transmission resource assignmentinformation segments included in the R-MAP information; and for each ofthe total number of transmission resource assignment informationsegments; transmitting information defining a particular configurationof a transmission resource or an assignment of the transmissionresource, for at least one frame of the series of frames.

In some embodiments, transmitting R-MAP information comprisestransmitting the R-MAP information in a downlink sub-frame of the atleast one frame.

In some embodiments, transmitting the R-MAP information in a downlinksub-frame further comprises transmitting the R-MAP information in adownlink relay station (DL RS) zone of the downlink sub-frame.

In some embodiments, the further comprising transmitting a relay zoneframe control header (R-FCH) channel prior to transmitting the R-MAPinformation, the R-FCH comprising a length of the R-MAP information andmodulation and coding rate of the R-MAP information.

In some embodiments, transmitting information defining a particularconfiguration of a transmission resource or an assignment of thetransmission resource comprises transmitting a relay station identifier(RSID) to identify the at least one relay station for which theassignment is being made.

In some embodiments, transmitting a relay station identifier (RSID) toidentify the at least one relay station comprises: transmitting aunicast RSID for assigning a resource to a single relay station; andtransmitting a broadcast RSID for assigning a resource to a more thanone relay station.

In some embodiments, transmitting information defining a particularconfiguration of a transmission resource or an assignment of thetransmission resource comprises transmitting at least one of:configuration information for defining a basic resource unit (BRU) to beassigned; configuration information for defining a region oftime-frequency of the at least one frame to be assigned; assignmentinformation for assigning at least on BRU; and assignment informationfor assigning at least one region of time-frequency of the at least oneframe.

In some embodiments transmitting configuration information for defininga basic resource unit (BRU) to be assigned comprises transmitting: alength of the configuration information; a first OFDM symbol indexindicating an index of an OFDM symbol at which a downlink relay station(DL_RS) Zone begins; a first number of OFDM symbols indicating a numberof OFDM symbols which the DL_RS Zone occupies; an indication of a numberof sub-channels which are included in each downlink basic resource unit(DL BRU) of the DL_RS Zone; a second OFDM symbol index indicating anindex of an OFDM symbol at which an uplink relay station (UL_RS) Zonebegins; a second number of OFDM symbols indicating a number of OFDMsymbols which the UL_RS Zone occupies; an indication of a number ofslots which are included in each uplink basic resource unit (UL BRU) ofthe UL_RS Zone; an indication of a number of frames before theconfiguration takes effect, starting from the current frame.

In some embodiments, transmitting configuration information for defininga basic resource unit (BRU) to be assigned comprises transmittingconfiguration information in the form of an Information Element (IE)consistent with the following format:

Syntax Size Notes RS Zone BRU Configuration IE { Type 4 bits 0x00 Length4 bits Length in bytes OFDM symbol index for 8 bits Indicates the OFDMsymbol DL_RS Zone index starting a DL_RS Zone Number of OFDM symbols 4bits Indicates the number of OFDM symbols a DL_RS Zone occupies DL BRU 4bits Indicates the number of sub-channels a DL BRU includes OFDM symbolindex for 8 bits Indicates the OFDM symbol UL_RS Zone index starting aUL_RS Zone Number of OFDM symbols 4 bits Indicates the number of OFDMsymbols a UL_RS Zone occupies UL BRU 4 bits Indicates the number ofslots a UL BRU includes Number of frames before 4 bits Indicates thenumber of effective frames before the configuration takes effect(starting from the current frame) }

In some embodiments, transmitting configuration information for defininga region of time-frequency of the at least one frame to be assignedcomprises transmitting: a length of the configuration information; afirst OFDM symbol index indicating an index of an OFDM symbol at which aDL_RS Zone begins; a first number of OFDM symbols indicating a number ofOFDM symbols which the DL_RS Zone occupies; an indication of a number ofregions defined in the DL_RS Zone; for each region of the number ofregions defined in the DL_RS Zone: an indication of a number ofsub-channels in the DL region; a second OFDM symbol index indicating anindex of an OFDM symbol at which an UL_RS Zone begins; a second numberof OFDM symbols indicating a number of OFDM symbols which the UL_RS Zoneoccupies; an indication of a number of regions defined in the UL_RSZone; for each region of the number of regions defined in the UL_RSZone: an indication of a number of slots an uplink basic resource unit(UL BRU) includes; an indication of a number of frames before theconfiguration takes effect, starting from the current frame.

In some embodiments, transmitting configuration information for defininga region of time-frequency of the at least one frame to be assignedcomprises transmitting configuration information in the form of an IEconsistent with the following format:

Syntax Size Notes RS Zone Region Configuration IE { Type 4 bits 0x00Length 4 bits Length in byte OFDM symbol index for 8 bits Indicates theOFDM symbol DL_RS Zone index starting a DL_RS Zone Number of OFDMsymbols 4 bits Indicates the number of OFDM symbols a DL_RS Zoneoccupies Number of DL region 6 bits Indicates the number of regionsdefined in DL_RS Zone For (i=0;i<Number of regions; i++){ Number ofsubchannels } 4 bits Indicates the number of sub-channels the regionincludes OFDM symbol index for 8 bits Indicates the OFDM symbol ULRS_Zone index starting a UL_RS Zone Number of OFDM symbols 4 bitsIndicate the number of OFDM symbols a UL_RS Zone occupies Number of ULregion 6 bits Indicates the number of regions defined in UL_RS Zone For(i=0;I<Number of region; i++){ Number of slots } 4 bits Indicates thenumber of slots the region includes Number of frames before 4 bitsIndicates the number of effective frames before the configuration takeseffect (starting from the current frame) }

In some embodiments, transmitting assignment information for assigningat least on BRU comprises transmitting: a relay station identifier(RSID) indicating a particular destination relay station to which thetransmission resource is assigned; an indication of a number of DL BRUassigned to an RS identified with the RSID; an indication of themodulation and coding scheme (MCS) used for the transmission resourceassigned to the RS identified with the RSID; an indication of a numberof UL BRU assigned to the RS identified with the RSID; an indication ofthe MCS used for the transmission resource assigned to the RS identifiedwith the RSID.

In some embodiments, transmitting assignment information for assigningat least on BRU comprises transmitting configuration information in theform of an IE consistent with the following format:

Syntax Size Notes RS BRU Resource Assignment IE { Type 4 bits 0x01 RSID8 bits Relay station ID Number of DL BRU 6 bits Indicates the number ofDL BRUs assigned to an RS identified by RSID DL MCS 4 bits Indicates themodulation and coding scheme (MCS) to be used in the resource assignmentfor the RS identified by RSID Number UL BRU 6 bits Indicates the numberof UL BRUs assigned to an RS identified by RSID UL MCS 4 bits Indicatesthe MCS to be used in the resource assignment for the RS identified byRSID }

In some embodiments, transmitting assignment information for assigningat least on region of time-frequency of the at least one frame comprisestransmitting: a relay station identifier (RSID) indicating a particulardestination relay station that the resource assignment is directed to; aDL region identifier (DL region ID) identifying a DL region assigned tothe RS identified by the RSID; an indication of the MCS used for the DLregion identified by the DL region ID; a UL region identifier (UL regionID) identifying a UL region assigned to the RS identified by the RSID;an indication of the MCS used for the UL region identified by the DLregion ID.

In some embodiments, transmitting assignment information for assigningat least on region of time-frequency of the at least one frame comprisestransmitting configuration information in the form of an IE consistentwith the following format:

Syntax Size Notes RS Region Resource Assignment IE { Type 4 bits 0x01RSID 8 bits Relay station ID DL region ID 6 bits Indicates anidentification of a DL region assigned to an RS identified by RSID DLMCS 4 bits Indicates the MCS to be used in the resource assignment forthe RS identified by RSID UL region ID 6 bits Indicates anidentification of an UL region assigned to an RS identified by RSID ULMCS 4 bits Indicates the MCS to be used in the resource assignment forthe RS identified by RSID }

In some embodiments, transmitting R-MAP information comprisestransmitting multiple R-MAP, each R-MAP for a respective one RS ormultiple RSs with similar channel qualities.

Other aspects and features of the present invention will become apparentto those ordinarily skilled in the art upon review of the followingdescription of specific embodiments of the invention in conjunction withthe accompanying figures.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention will now be described with reference to theattached drawings in which:

FIG. 1 is a block diagram of an example of a network including a basestation, relay stations and mobile stations;

FIGS. 2 and 3 are schematic diagrams of frame structures provided byembodiments of the invention;

FIG. 4 is a set of schematic diagrams of bin construction for even andodd bin sizes;

FIG. 5 is a set of schematic diagrams of two specific sub-channeldefinitions;

FIG. 6 is a schematic diagram of a frame structure according to anembodiment of the invention;

FIG. 7 is a set of schematic diagrams of bin construction for twodifferent bin sizes, and for bins with and without pilots;

FIG. 8 is a set of schematic diagrams of two specific sub-channeldefinitions;

FIG. 9 is a group of schematic diagrams of pilot patterns to be used bya relay station according to some embodiments of the invention;

FIG. 10 is a block diagram of a cellular communication system;

FIG. 11 is a block diagram of an example base station that might be usedto implement some embodiments of the present invention;

FIG. 12 is a block diagram of an example wireless terminal that might beused to implement some embodiments of the present invention;

FIG. 13 is a block diagram of a logical breakdown of an example OFDMtransmitter architecture that might be used to implement someembodiments of the present invention;

FIG. 14 is a block diagram of a logical breakdown of an example OFDMreceiver architecture that might be used to implement some embodimentsof the present invention;

FIG. 15 is a flow chart describing a method of transmitting frames in anOFDM system including relay stations according to an embodiment of theinvention; and

FIG. 16 is a flow chart describing a method of transmitting R-MAPinformation according to an embodiment of the invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS OF THE INVENTION

In accordance with embodiments of the invention, various physical layerdesigns and procedures are provided for enabling relay basedcommunications that may find applications in an IEEE 802.16 basednetwork. The concepts described herein are not, however, limited in thisregard and may be applicable to any OFDM based systems, such as 3GPP and3GPP2 evolutions.

FIG. 1 shows an example of a wireless system, for example an OFDMnetwork that includes relays. Shown is a base station (BS) 130 that isin communication with one or more mobile stations (MS), only one shownMS-1 132, and one or more first tier relay stations (RS), only one shownRS-1 138. Some of the first tier (one hop away from BS) relay stationsare in communication with one or more second tier (two hops away fromBS) relay stations. RS and MS the same number of hops away from the BSare said to be in the same tier. In the illustrated example RS-1 138 isin communication with second tier RS-2 140. Each relay station can serveone or more mobile stations. For example, RS-1 138 is in communicationwith MS-2 134 and RS-2 140 is in communication with MS-3 136. In theparticular example, there is a two-tier relay structure, such that thereis a maximum of three hops to reach a mobile station. Larger numbers ofhops are contemplated. Furthermore, the specific network of FIG. 1 is tobe considered only an example. More generally, an arbitrary arrangementof base stations, relay stations, and mobile stations is contemplated.The mobile stations will change over time due to their mobility. Someembodiments support only fixed relays; others support mobile relays,while further embodiments support both fixed and mobile relays.

Referring to FIG. 2, shown is a specific frame structure for handlingthe presence of relays in an OFDM communication system. FIG. 2 alsoincludes an example of a network 1600 including relay stations RS-1 1618and RS-2 1620, base station BS 1610 and mobile stations MS-1 1612, MS-21614 and MS-3 1616, similar to FIG. 1 to clearly illustrate thecorrespondence of the frame structure to the base station BS and relaystations RS-1 and RS-2.

In FIG. 2, the horizontal direction of the frame structure is time,representing multiple OFDM symbols, while the vertical direction isfrequency, representing multiple OFDM sub-carriers. In the first row2030, communication from the perspective of BS 1610 is shown; in thesecond row 2035, communication from the perspective of a first tierrelay station RS-1 1618 is shown; in the third row 2040, communicationfrom the perspective of a second tier relay station RS-2 1620 is shown.In the time direction, frames are defined, each consisting of multipleOFDM symbols. FIG. 2 is an example of four sequential TDD frames in apotential series of frames in which a respective DL sub-frame and arespective UL sub-frame have been combined together to form each of thetwo TDD frames.

In the embodiment illustrated in FIG. 2, a DL/UL (downlink/uplink)duplex structure is employed. Each frame 2050,2052,2054,2056 includes aDL sub-frame 2024,2026 used for DL communication and a UL sub-frame2025,2027 used for UL communication. The size of these sub-frames can bestatically or dynamically defined. In FIG. 2 both sides of acommunication are shown. More specifically, a portion of a frame used totransmit from a first entity, for example BS 1610, to a second entity,for example RS-1 1618, is shown in both the frame structure 2030 for BS1610 and the frame structure 2035 for RS-1 1618.

The frames are divided into first and second groups of frames. In theillustrated example, the first group is the odd frames 2050,2054 and thesecond group is the even frames 2052,2056 but other definitions arepossible. In FIG. 2, the first group of frames is used for UL and DLcommunication between BS 1610 and its first tier RSs (RSs one-hop awayfrom BS), for example RS-1 1618 and for communications (not shown)between the BS 1610 and MS directly served by the BS, for example MS-11612.

In addition, in some embodiments, the first group of frames is also usedfor communication between the second tier RSs (two-hops away from theBS), for example RS-2 1620, and MS associated with the second tier RSs,for example MS-3 1616. While it is not shown, in some embodiments RS-21620 may communicate with a third tier RS as well as MS-3 1616. Thisassumes interference from transmissions from the BS will notsignificantly effect transmissions from second tier RSs.

In FIG. 2, the second group of frames 2052,2056 is used for UL and DLcommunication between the first tier RS RS-1 1618 and any RS/MS it iscommunicating with. This would include, for example, communicationsbetween RS-1 and RS-2 1620, and communications between RS-1 and MS-21614 (not shown).

In some embodiments, the BS 1610 is also permitted to communicate duringthe second group of frames with mobile stations where the power of thetransmissions is controlled. For example, the power of the transmissionmay be at a reduced power level with mobile stations that are closer tothe base station, so as not to interfere with the relay communications.

In some embodiments, the RSs are also permitted to communicate with MSsduring either the first or second groups of frames where the power ofthe transmissions is controlled. For example, as indicated in FIG. 2,when a first tier RS 1618 is scheduled to communicate with a BS 1610during a first group of frames 2050 and is scheduled to communicate witha second tier RS 1620 and with at least one MS 1614 communicating withthe first tier RS 1618 during a second set of frames 2052, the firsttier RS 1618 can also communicate with the at least one MS 1614communicating with the first tier RS 1618 during the first set of frames2050 as well. This communication occurs in the first and second groupsof frames in a portion of the respective frames assigned for DL and ULcommunication with MSs.

In some embodiments, in order to ensure backwards compatibility with MSthat support 802.16e, each RS, after network entry, transmits a preamble2060 and a frame control header (FCH) channel 2062 on every frame asshown.

In systems that do not use relay stations, the BS transmits a preamblethat is used by mobile stations to measure radio propagation environmentand enable MS cell selection. In 802.16e, this preamble is transmittedat the start of every DL sub-frame. In the illustrated example of FIG. 2the preamble is identified by reference character 2064. The preamble isfollowed by the FCH channel, identified in FIG. 2 by reference character2065. The FCH provides initial information about the contents of the DLand/or UL sub-frames. For example, the FCH may contain information aboutthe size of the MAP information following the FCH. When relay stationsare present, they also transmit such a preamble in a similar manner sothat MS cell selection can be performed as before. This preamble isreferred to as a “normal preamble”. A problem with this approach is thatan RS needs to be able to look at a received preamble and transmit apreamble at the same time. An embodiment of the invention provides amethod of a preamble transmission by the RS that enables RS radioenvironment measurement without interrupting MS cell selection.

In a particular implementation, a new preamble, referred to as anRS_preamble since it is transmitted by the RS only and not the BS, istransmitted in every Nth frame, where N≧1, once the RS enters thenetwork. In some embodiments, the RS_preamble is transmitted in additionto the normal preamble. In some embodiments, frames are as defined in802.16e, but other frame definitions are contemplated.

In some embodiments, the RS_preamble is transmitted within a ULsub-frame for TDD implementations or a UL sub-frame for FDDimplementations. Note this is in contrast to the normal preamble that istransmitted during the DL sub-frame. A pseudo-random noise (PN) sequencefor each respective RS preamble may be the same as that of an assignednormal preamble or the PN sequence may be different.

The RS's transmission and receiving of this RS_preamble is synchronizedso that at each RS_preamble transmission time, RSs that need to listento preambles are not transmitting preambles at the same time as they arereceiving the preambles. For example, first tier RSs can simultaneouslytransmit their preambles during a first preamble transmission period,and second tier RSs can monitor these; similarly, second tier RSs cansimultaneously transmit their preambles during a second preambletransmission period, and first and/or third tier RSs when present canmonitor these. In a particular example, first tier RSs transmit theirpreamble during odd UL sub-frames or UL frames, and second tier RSstransmit their RS_preamble during even UL sub-frames or UL frames.

In some embodiments RS_preamble reuse within a cell is employed.

In some embodiments, for the multiple carrier case such as the exampleof FIG. 2, a common channel is defined as a primary channel fortransmitting an RS_preamble for each respective RS to determine a radioenvironment measurement. The radio environment measurements are used to,for example establish topology, transmit broadcast traffic and RSrelated control messages, and negotiate or declare the transmission andreceiving schedule on another channel.

In some embodiments, having defined the first and second groups offrames, RS Zones are defined in the time domain to enable more efficientsub-channelization. More specifically, a DL_RS Zone is defined fordownlink transmission (from a base station or a relay to another relay)and a UL_RS Zone is defined for uplink transmission (from a relay toanother relay, or from a relay to BS. Remaining resources are availablefor communication with mobile stations. For example the DL sub-frame mayinclude a DL_MS zone having a set of one or more OFDM symbolsspecifically targeted for reception by one or multiple MS and the ULsub-frame may include a UL_MS zone having a set of one or more OFDMsymbols for receiving from one or multiple MS.

In the illustrated example of FIG. 2, four TDD frames2050,2052,2054,2056 are shown. Only TDD frames 2050 and 2052 will bedescribed in detail. TDD frame 2050 is composed of DL sub-frame 2024during which downlink transmissions from the BS 1610 occur and a ULsub-frame 2025 during which uplink transmissions to the BS 1610 occur.Similarly, TDD frame 2052 is composed of DL sub-frame 2026 during whichdownlink transmissions from first tier RS 1618 occur and a UL sub-frame2027 during which uplink transmissions to second tier RS 1620 occur. Alegend indicating differing shadings for the differing zone types isgenerally indicated at 2068.

During the DL sub-frame 2024, the frame structure 2030 for the BS 1610includes the preamble 2064 and FCH 2065. In some embodiments, the FCH isconsistent with 802.16e. The frame structure 2030 includes a DL_RS zone2076 that includes a relay station R-MAP 2074 for transmission to relaystations such as RS-1 1618. The DL_RS zone 2076 may also include a relaystation frame control header (R-FCH) channel 2075 that contains framecontrol header information specifically for the DL and UL_Zones, forexample modulation and coding scheme information pertaining to theR-MAP. The DL sub-frame 2024 of frame structure 2030 may also include aDL_MS zone (not shown) for transmission directly to mobile stations suchas MS-1 1612.

During the DL sub-frame 2024, the frame structure 2035 for the RS-1 1618includes a preamble 2060 and FCH 2062. In some embodiments the preambleis the RS_preamble described above. In the illustrated example, an areaof the DL sub-frame 2024 in frame structure 2035 is shown for receivingthe DL-RS zone 2076 that includes the R-MAP 2074. An area is also shownfor receiving the R-FCH 2075. The DL sub-frame 2024 of frame structure2035 may include a DL_MS zone (not shown) for transmission directly tomobile stations such as MS-2 1614 as well as RS radio switching periods(not shown). During the radio switching periods, the RS switches itsradio from transmitting to receiving or vice versa.

During the DL sub-frame 2024, the frame structure 2040 for the RS-2 1620includes a preamble 2060 and FCH 2062. The DL sub-frame 2024 of framestructure 2040 may include a DL_MS zone (not shown) for transmissiondirectly to mobile stations such as MS-3 1616. There may also be RSradio switching periods.

During the UL sub-frame 2025, the frame structure 2030 for the BS 1610includes an area of the UL sub-frame 2025 for receiving UL_RS zone 2078transmissions from relay stations such as RS-1 1618. The UL sub-frame2025 of frame structure 2030 may also include a UL_MS zone (not shown)for receiving from mobile stations such as MS-1 1612.

During the UL sub-frame 2025, the frame structure 2035 for the RS-1 1618includes the UL RS zone 2078 for transmission from relay stations suchas RS-2 1620. The UL sub-frame 2025 of frame structure 2035 may alsoinclude a UL_MS zone (not shown) for receiving from mobile stations suchas MS-2 1614. There may also be RS radio switching periods.

During the UL sub-frame 2025, the frame structure 2040 for the RS-2 1620may include a UL_MS zone (not shown) for receiving from mobile stationssuch as MS-3 1616.

During the DL sub-frame 2026, the frame structure 2030 for the BS 1610includes a preamble 2064 and FCH 2065. The DL sub-frame 2026 of framestructure 2030 may also include a DL_MS zone (not shown) fortransmission directly to mobile stations such as MS-1 1612.

During the DL sub-frame 2026, the frame structure 2035 for the RS-1 1618includes a preamble 2060 and FCH 2062. The frame structure 2035 includesa DL_RS zone 2080 that includes an R-MAP 2082 for transmission to relaystations such as RS-2 1620. The DL_RS zone 2080 may also include anR-FCH 2081. The DL sub-frame 2026 of frame structure 2035 may include aDL_MS zone (not shown) for transmission directly to mobile stations suchas MS-2 1614 as well as RS radio switching periods.

During the DL sub-frame 2026, the frame structure 2040 for the RS-2 1620includes a preamble 2060 and FCH 2062. In the illustrated example, anarea of the DL sub-frame 2026 in frame structure 2035 is shown forreceiving the DL_RS zone 2080 that includes the R-MAP 2082. An area isalso shown for receiving the R-FCH 2081. The DL sub-frame 2026 of framestructure 2040 may include a DL_MS zone (not shown) for transmissiondirectly to mobile stations such as MS-3 1616. There may also be RSradio switching periods.

During the UL sub-frame 2027, the frame structure 2030 for the BS 1610may include UL_MS zone (not shown) for receiving from mobile stationssuch as MS-1 1612.

During the UL sub-frame 2027, the frame structure 2035 for the RS-1 1618includes an area of the UL sub-frame 2027 for receiving a UL_RS zone2084 from relay stations such as RS-2 1620. The UL sub-frame 2027 offrame structure 2035 may also include UL_MS zone (not shown) forreceiving from mobile stations such as MS-2 1614. There may also be RSradio switching periods.

During the UL sub-frame 2027, the frame structure 2040 for the RS-2 1620includes a UL_RS zone 284 for transmitting to relay stations, such asRS-1 1618. The UL sub-frame 2027 of frame structure 2040 may alsoinclude a UL_MS zone (not shown) for receiving from mobile stations suchas MS-3 1616.

Corresponding zones for transmitting/receiving are defined in the firstframe 2050 for the first tier RS RS-1 1618 and the BS 1610 in framestructures 2030,2035. During this time, the second tier relay RS-2 1620is only communicating with MS, for example MS-3 1616, so no zones aredefined. Similar zones are defined for communication between RS-1 1618and RS-2 1620 during each of the second group of frames 1652, includingthe second and fourth frames 2052,2056 in frame structures 2035,2040.

The size of the RS Zone and a starting location of the RS zone intime-frequency within a frame can be defined for example by a) a fixedsize, b) slowly changed in size through use of a management MAC message,and c) dynamically changed in size and forecast by BS and DLtransmitting RSs a few frames before the change.

A general method for use in an OFDM communication system employing relaystations according to some embodiments of the invention will bedescribed with reference to FIG. 15. A first step 15-1 in the methodincludes dividing communications into frames each comprising multipleOFDM symbols. A second step 15-2 in the method includes dividing theframes into first and second groups of frames, the first group of framesbeing used for communication between a base station (BS) and first tierRSs one-hop away from the BS, and for communications between the BS andits respective mobile stations (MSs), the first group also being usedfor communication between RSs of a 2Nth tier and RSs of a 2N+1th tier,N>=1, the RSs of a 2Nth tier being 2N hops away from the BS, and any MSsthe RS of the 2Nth tier is communicating with, and the second group offrames being used for communication between RSs of a 2N−1th tier and theRSs of a 2Nth tier, the RSs of the 2N−1th tier being 2N−1 hop(s) awayfrom the BS, and any MSs the RS of the 2N−1 tier is communicating with.

Some embodiments provide for the reuse of OFDM symbols in multiplezones. Some embodiments provide for reuse between different tiers, whileothers provide for reuse within a tier. An example of reuse betweendifferent tiers in a hierarchical network is a BS transmitting duringOFDM symbol intervals, and an RS transmitting on the same OFDM symbolintervals assuming the transmissions will not interfere. Another exampleof reuse between different tiers in a hierarchical network is an RStransmitting during OFDM symbol intervals, and an RS in a different tiertransmitting on the same OFDM symbol intervals assuming thetransmissions will not interfere.

An example of reuse within a tier in a hierarchical network is an RStransmitting during OFDM symbol intervals, and another same tier RStransmitting on the same OFDM symbol intervals assuming thetransmissions will not interfere.

DL Preamble Transmission

In some embodiments, DL preambles are used to transmit PN codes in amanner consistent with current 802.16e definitions. These provide for atotal of 114 PN sequences (57×2) and 32 IDcell definitions. In someembodiments, each transmitting station (BS and RS) is physicallydifferentiated within a geographic area by a respective distinctpreamble PN sequence for switching purposes. Each respective preamble PNsequence implies a particular IDcell. Thus, each RS is assigned adedicated PN sequence. This enables a preamble sequence space reuse thatis larger than what 802.16e defines. The preamble can be transmittedwithin the network synchronized in a manner to enable serving stationselection.

In some embodiments, the 802.16e standard is adapted to be used in thismanner by modifying management messages to be used by the relay stationwhen it enters the network. In some embodiments, the management messagesare REG-REQ/RSP (registration request/response) messages. For example,the REG-REQ/RSP messages can be modified to include an assigned PN indexinformation field, a DL_PermBase information field, and a PRBS_IDinformation field. DL_PermBase and PRBS_ID are index numbers used fordata randomizations in the 802.16e standard. They are essentially linkedto the Base station ID to ensure that each base station randomizes datain different manner. Specifically, DL_PermBase is used in relation tophysical sub-channel to logical sub-channel mapping and PRBS_ID is usedin relation to data scrambling.

In some embodiments, an algorithm is employed to perform PN indexselection. The algorithm selects and assigns to an RS the PN indexselection to minimize IDcell collision. The algorithm also may assignDL_PermBase and PRBS_ID values.

For the purpose of routing, a station (BS and RS) is identified by a BSID (base station identification) in a MAC management message. For thispurpose, each RS is assigned a BS ID (48 bits). In some embodiments, the802.16e standard is adapted to be used in this manner by modifying theREG-REQ/RSP to include the assigned BS ID.

Various options exist for PN assignment for a mobile relay station (MRS)preamble. In some embodiments, the preamble PN index does not changeduring handover of an MRS from a BS serving first cell to a BS serving asecond cell as the MRS moves between the first and second cells. Thisinvolves defining a system reserved for a sub-set of PN indexes for theMRS so as to avoid collision when the MRS moves across the network. Insome embodiments, the preamble is changed or re-assigned duringhandover, and no PN needs to be reserved for the MRS. In this case, theMSs associated with the MRS need to be informed of the change or theymust perform re-synchronization. In a particular example, this isachieved by modifying a message, such as a mobile handoff messageresponse (MOB_MSHO_RSP) to include a preamble PN index.

RS 802.16e Preamble Transmission

In some embodiments, each RS is configured to transmit a preamble tofacilitate a MS to perform cell selection and handoff, as well as topotentially aid in other functionality. A specific example of such apreamble is that specified by 802.16e, but others may be used. In theexample that follows, 802.16e preambles are assumed, but similarpreamble re-use can be applied to any finite preamble resource. Withpreambles based on 802.16e-2005, there are a total of 114 preambles(identified by preamble as characterized by IDcell, segment and PNsequence) for 1024 mode and 512 mode. This preamble resource pool isshared between base stations and the RSs which are configured totransmit 802.16e preamble.

Preamble Selection

During RS initial network entry, an RS performs the cell selection in asimilar manner that a MS does. In some embodiments, this procedure isenhanced to enable the RS assistance in preamble PN sequence selection.

To begin, the RS maintains information identifying a set of possiblepreambles for use in the system to be measured. In an example approachto achieving this, the relay station maintains preamble informationconsisting for example of an entry for each preamble with each entryhaving a preamble index corresponding to the PN sequence. The RSmeasures the strength of each of the possible preambles and records thestrength of each. The strength of each preamble may be recorded in atable for the corresponding entry. The longer the time taken for thismeasurement, the more the impact of fading will be minimized. When themeasurement procedure is finished, for example when some number offrames has been measured, the RS determines its serving station (a basestation or possibly another relay station) based on these measurements.The particular criteria here are not relevant and any method of cellselection can be employed.

Having performed cell selection, preamble selection is performed toselect the preamble that will be transmitted by the relay station. Insome embodiments, the RS uses the strength information to determine acandidate preamble pool for the purpose of a preamble selection. In someembodiments, the candidate preambles in the candidate pool are thosepreambles whose strengths measured by this RS are lower than apre-defined threshold. More complicated selection procedures are alsocontemplated; for example any preamble below a first threshold up tosome number and any preamble below a second threshold up to some numberand so on; the lowest N below a particular threshold, etc. The RS thenselects one preamble from the candidate pool and reports this back toits serving base station, either directly or via other relay stations.More generally, the RS may select some number M of preambles andindicate these to its serving base station. The selected preambles canbe indicated by the preamble index. The base station may agree or deny asingle selected preamble. In some implementations, the base stationsignals a determination of one or more preambles to the relay station.In some embodiments, multiple preambles are selected by the relaystation, and the base station signals a selection of one of these.

In some embodiments, preamble selection is cooperative in that both therelay station and the base station participate. To begin, the RS reportspreamble measurement information to its BS. This may for example containa list that includes all the preamble indexes whose strength measured bythe RS are higher and/or lower than a pre-defined threshold, but otherinformation may alternatively be fed back to the BS.

The BS assigns a preamble based on the information from the listreported by this RS, for example by selecting one on the list or one noton the list depending on what is fed back. In some embodiments, the BStakes into account other available information such as what preamble(s)are currently in use within the cell and in use in neighbouring cell(s),assuming this information is made available by neighbour BSs. Suchinformation may be made available for example through backhaulconnections.

Advantageously, by reasonable setting of threshold and measurement time,preamble collision (multiple devices attempting to use the same preamblein an overlapping coverage region) can be reduced, and the need for acomplex preamble plan can be avoided.

In an example implementation, a Config-REQ/RSP MAC management messageutilized. In the Config-REQ/RSP MAC management message the 4 bitreserved field is replaced with “RS_Zone Prefix location” The “RS_ZonePrefix location” indicate the OFDM symbol index relative to thebeginning of current frame in units of 2 OFDM symbols.

In some embodiments, preamble strength measurement information, madeavailable by mobile stations and/or relay stations is used by the basestation to perform resource re-allocation. To begin, mobile stationsreport the strengths of preambles transmitted by relays, and moregenerally the strength of all the preambles that it can measure. In someembodiments, a mobile station may not necessarily distinguish between apreamble transmitted by a BS and a preamble transmitted by an RS andreports the signal strength of both. However, when a BS receives thesignal strength measurements it knows which measurement is for the BSpreamble and which measurement is for the RS preamble. The BS then usesthis information to intelligently perform resource re-use between therelay stations. For example, when a MS reports negligible strength of apreamble transmitted by a one RS and good signal strength from a secondRS, the signals transmitted by that first and second RSs may notinterfere with each other and as such resources that are in use by theneighbouring base station. Examples of resources that can be allocatedin this manner include resources within OFDM frames—for exampleparticular sub-carriers over particular OFDM symbols or frames.

In a specific example of performing resource re-use based on thestrength measurements, if a first MS reports a good signal strength froma first RS and poor signal strength from a second RS, and a second MSreports a good signal strength from the second RS and poor signalstrength from the first RS, then the same or at least partiallyoverlapping resources, can be assigned at the first and second RS fortransmitting to the first and second MS with the understanding that thiswill not result in interference.

More generally, resources can be allocated at a first relay station tothe mobile station that are also being allocated at a second relaystation whose preamble signal strength measurement is s below a definedthreshold.

The embodiment described above, and the specific example thereof shownin FIG. 2 all assume a TDD separation between DL and UL transmissions.Further embodiments are provided that parallel the embodiments describedwith the exception that the separation between DL and UL transmissionuses FDD. All of the examples described above also can be modified tothis context; the only difference is that rather than having ULsub-frames and DL sub-frames that are transmitted during separate timeintervals, UL frames and DL frames are simultaneously transmitted, buton different frequencies.

R-MAP

In some embodiments, an R-MAP is transmitted to indicate thetransmission resource configurations and assignments for the DL_RS zoneand/or the UL_RS zone. In some embodiments, the R-MAP is transmitted byeach DL transmitting BS and RS in one or more DL sub-frames.

In some embodiments, transmitting an R-MAP in a frame includestransmitting information regarding transmission resource assignment forrelay stations one hop away from the station transmitting the R-MAP.Transmission resource assignment information transmitted for each relaystation one hop away includes one or more of: identification informationto identify the relay station the resource assignment information isdirected to; transmission resource configuration information todetermine how the transmission resource is configured; transmissionresource location information to identify a location in the frame of thetransmission resource; transmission resource size information toidentify a size of the transmission resource; and modulation and codescheme (MCS) information for the respective transmission resources. Insome embodiments, location information is provided in the form of afixed offset relative to the beginning of a frame. In some embodiments,location information is provided in the form of a fixed offset relativeto the RS Zone.

Multiple R-MAPs may be transmitted, in which each respective R-MAPincludes resource assignments for one or more RS sharing similar channelqualities.

RS DL Resource Allocation Methods

The RS DL resource is a transmission resource used for communicationfrom a BS to an RS and from an RS to its next hop RS. In someembodiments, when the RS is forwarding traffic for multiple MSs(aggregated traffic), the aggregated traffic presents a less burstynature than traffic dedicated to a single MS. As such, the trafficpattern is similar to a connection-oriented connection. Furthermore,since many RSs have a fixed position, a change in channel conditionsfrom the BS to RS and RS to next hop RS may be less frequent than thatof a BS to MS or RS to MS, and the channel may remain unchanged for aduration that is longer than a duration of a frame, for example a frameduration defined by 802.16e. Because of these distinctions, a resourceassignment mechanism can be different from that currently supported by802.16e for MS.

In some implementations, a persistent DL RS related resource assignmentmechanism is employed. With such a mechanism, a BS or an RS can assign aDL resource to its next hop RS for a period of time longer than a frame,a frame being the nominal period for assignment, for example accordingto current 802.16e specifications. The resource assignment can beupdated from time to time. Variables of the resource assignment include,for example, a target relay station identifier (RSID) and any one ormore of resource size, resource location and MCS. In some embodiments,the resource assignment can be supplemented beyond an existingpersistent resource assignment from time to time. The resource can alsobe terminated when appropriate, such as when the resource is no longerneeded.

In some implementations, the RS is assigned a dedicated feedback channelfor a period of time. The feedback channel may be present every N frameswhere N is a number greater than or equal to one. The feedback channelcan be used for various purposes. For example, the RS may use thisfeedback channel to send a channel quality indicator, a feedback headeror a BW (bandwidth) request periodically.

The following type of messaging can be employed to implement the abovemethod, but other implementations are possible.

The R-MAP in the RS Zone is used for a parent station to signal aresource assignment in the RS Zone to a next hop relay station. Thisincludes, for example, BS to RS and RS to next hop RS.

In order to define an efficient resource assignment for a relay station,the difference between the assignment to RS and to MS is identified. Insome embodiments, each RS is addressed by a relay station identifier(RSID), having a fixed length in bits, which is shorter in number ofbits than a connection identifier (CID) used to identify a connectionbetween BS and MS.

Generally speaking, RS traffic is less bursty and an amount of trafficis larger than that of a MS due to the fact that the traffic of an RS isaggregated traffic of multiple MSs. Resource allocation for an RS caninclude either one of or both of DL and UL assignments. Resourcegranularity may be larger than a single sub-channel (for downlinktransmission) and/or a single slot (for uplink transmission), asdescribed above. Methods for defining a resource configuration will bedescribed in further detail below.

In some embodiments, the R-MAP is implemented without defining aseparate DL R-MAP and a separate UL R-MAP in the respective RS DL and RSUL zones.

In some embodiments, the R-MAP can be used for unicast resourceassignment by using a unicast RSID and/or a broadcast resourceassignment by using a broadcast RSID.

A resource is assigned using basic resource units (BRUs), which may be asingle sub-channel (for downlink), a single slot (for uplink), multiplesub-channels or multiple slots. The BRU configuration definition can bea broadcast within the R-MAP, for example an RS Zone configurationinformation element (IE) described in further detail below.

In some embodiments, unicast resource assignment information having aformat as concise as possible is defined to reduce unnecessary overhead.In some embodiments, a fixed length. IE is used, as will be described inexamples below.

The R-MAP can use a similar format used for DL MAP and UL MAP formats asdefined in IEEE802.16e-2005. However, this is not very efficient sincesome fields in the DL MAP and UL MAP formats are redundant.

The R-MAP can be used to signal the resource assignments and othercontrol information included in the relay zones transmitted by the BS orRS. In some embodiments, the R-MAP is sent in the first transmittedRS_DL Zone. In some embodiments, the message is preceded by an R-FCH(Relay frame control header). Information such as the length of theR-MAP message and modulation and coding rate are indicated in the R-FCH.In some embodiments, the message is not preceded by a MAC header andmessage field type.

In some embodiments, the R-MAP message may transmit transmissionresource assignment information segments defining resource assignmentinformation. The R-MAP may information such as the length of the R-MAPand for each transmission resource assignment information segmenttransmitted in the R-MAP, an indication of the type of information andwhat the information is. For example, a transmission resource assignmentinformation segment may be downlink MAP information, uplink MAPinformation and/or relay station link (R-link) specific information. Insome embodiments, the respective transmission resource assignmentinformation segments are transmitted in the form of an informationelement (IE). An information element is a portion of a message used toprovide information to a relay station receiving a transmission on thetransmission resource. Table 1 illustrates an example of an R-MAPmessage format with particular field sizes and field contents.

TABLE 1 An example of an R-MAP message format Syntax Size Notes R-MAPformat { Length 11 bits Length of R-MAP For (i= 0; i<Number of For eachIE of a total IEs; i++) { number of IEs IE type  2 bits 0b00: DL MAP IE0b01: UL MAP IE 0b10: R-link specific IE 0b11: reserved If (IE type = =00) { DL MAP IE } Variable Elseif (IE type = = 01){ UL MAP IE} VariableElseif (IE type = = 10) { R-link specific IE } Variable   } }

In the example of Table 1, an IE type is indicated by a two bit value asone of a DL MAP IE, a UL MAP IE, or an R-link specific IE. For example,each IE in the R-MAP is identified as one of the three types. Asindicated above the DL and UL MAP formats are not as efficient as theR-link specific format. Particular examples of R-link specific formatsare formats such as found in Tables 4-7 below.

In some embodiments, a message can be designated to be an R-MAP messageby sending an indication in the message that identifies the message isan R-MAP message. For example, a pre-defined message type can beassigned for identifying an R-MAP message. Such a message type value isimplementation specific and could be any accepted value known by the BS,RS and MS. In some of the following examples the message type value of67 indicating an R-MAP message will be used for example purposes.

TABLE 2 R-MAP message type Message Type name Message description 67RS_MAP Resource assignment message transmitted in RS_Zone

An R-MAP message format may include transmitting: an indication that thetype of message is an R-MAP message; a number of IEs included in themessage and for each of the number of IEs; and an IE defining aparticular resource configuration or resource assignment. In someembodiments, the R-MAP message is sent within the DL_RS Zone, forexample as described above with regard to FIG. 2. A further example ofan R-MAP message format is shown in Table 3.

TABLE 3 Another example of an R-MAP message format Syntax Size NotesR-MAP format { Message type = 67 8 bits Number of IEs 4 bits Indicatesthe number of IEs included For (I = 0; Number of IEs; I++){ R-MAP IEVariable } }

Utilizing an R-MAP message can generally be described as a method oftransmitting R-MAP information in at least one frame of a series offrames, each frame comprising multiple OFDM symbols, to indicateconfiguration of a transmission resource and/or assignment of thetransmission resource for downlink and uplink communication between abase station and a relay station one hop away from the base station orbetween a relay station and a next hop relay station.

A particular example of transmitting R-MAP information will be describedwith regard to FIG. 16. A first step 16-1 of the method of FIG. 16includes transmitting an indication that the information is R-MAPinformation. A second step 16-2 of the method includes transmitting atotal number of transmission resource assignment information segmentsincluded in the R-MAP information. A third step 16-3 of the methodincludes, for each of the total number of transmission resourceassignment information segments, transmitting information defining aparticular configuration of a transmission resource or an assignment ofthe transmission resource, for at least one frame of the series offrames.

Examples of various R-MAP IE formats that may be included in the R-MAPmessage will now be described. Tables 4 and 5 below are examples of IEsthat define the configuration or size of the BRUs and regions,respectively in the DL and UL_RS Zones. Tables 6 and 7 are examples ofIEs that define the resource assignment of the DL and UL_RS Zones.

RS_Zone Basic Resource Unit (BRU) Configuration IE

The RS Zone BRU configuration IE is used for a parent station tobroadcast to one or more next hop RS the RS Zone related zoneconfiguration information valid for an Nth frame count from the currentframe. These configurations include the locations of DL_RS Zone andUL_RS Zone with each respective frame and the BRU definition within eachof the DL and UL_RS Zones. The corresponding BRU assignment IE (forexample Table 6) uses a BRU as a basic RS resource assignment unit.Table 4 illustrates an example of an RS Zone BAU Configuration IE formatwith particular field sizes and field contents.

TABLE 4 RS Zone BRU Configuration IE format Syntax Size Notes RS ZoneBRU Configuration IE { Type 4 bits 0x00 Length 4 bits Length in bytesOFDM symbol index for 8 bits Indicates the OFDM symbol DL_RS Zone indexstarting a DL_RS Zone Number of OFDM symbols 4 bits Indicates the numberof OFDM symbols a DL_RS Zone occupies DL BRU 4 bits Indicates the numberof sub-channels a DL BRU includes OFDM symbol index for 8 bits Indicatesthe OFDM symbol UL_RS Zone index starting a UL_RS Zone Number of OFDMsymbols 4 bits Indicates the number of OFDM symbols a UL_RS Zoneoccupies UL BRU 4 bits Indicates the number of slots a UL BRU includesNumber of frames before 4 bits Indicates the number of effective framesbefore the configuration takes effect (starting from the current frame)}

The “Type” and “Length” fields indicate the length in bytes of the IEand the type of IE it is, for example an RS Zone BRU Configuration IE,as opposed to, for example, one of the other types of IE describedbelow.

The “OFDM symbol index for DL_RS Zone” field indicates an index of theOFDM symbol at which the DL_RS Zone begins. The first “Number of OFDMsymbols” field indicates a number of OFDM symbols which the DL_RS Zoneoccupies. The “DL BRU” field indicates a number of sub-channels which aDL basic resource unit (DL BRU) includes. The “OFDM symbol index forUL_RS Zone” field indicates an index of the OFDM symbol at which theUL_RS Zone begins. The second “Number of OFDM symbols” field indicates anumber of OFDM symbols which the UL_RS Zone occupies. The “UL BRU” fieldindicates a number of slots a UL basic resource unit (UL BRU) includes.The “Number of frames before effective” filed indicates a number offrames before the configuration takes effect, starting from the currentframe.

The size of each of the fields in Table 4 is indicated in bits. It is tobe understood that the field size is implementation specific and theprovided size is merely for example purposes.

The RS Zone BRU configuration may be particularly effective when eachBRU includes groupings of physical or logical sub-channels that have thesame number of sub-channels. However, in some embodiments, it may bebeneficial to have a configuration definition in which different regionsin the DL or UL resource have different respective numbers ofsub-channels. An example of providing such a configuration is the RSZone Region Configuration IE described below.

RS Zone Region Configuration IE

The RS Zone Region Configuration IE is used for a parent station tobroadcast to one or more next hop RS the RS Zone related configurationsvalid for an Nth frame count from the current frame. The configurationsinclude the locations of DL_RS Zone and UL_RS Zone and the regiondefinition within each of DL and UL_RS Zone. Table 5 illustrates anexample of an RS Zone Region Configuration IE format with particularfield sizes and field contents.

TABLE 5 RS Zone Region Configuration IE format Syntax Size Notes RS ZoneRegion Configuration IE { Type 4 bits 0x00 Length 4 bits Length in byteOFDM symbol index for 8 bits Indicates the OFDM symbol DL_RS Zone indexstarting a DL_RS Zone Number of OFDM symbols 4 bits Indicates the numberof OFDM symbols a DL_RS Zone occupies Number of DL region 6 bitsIndicates the number of regions defined in DL_RS Zone For (i=0;i<Numberof regions; i++){ Number of subchannels } 4 bits Indicates the number ofsub-channels the region includes OFDM symbol index for 8 bits Indicatesthe OFDM symbol UL RS_Zone index starting a UL_RS Zone Number of OFDMsymbols 4 bits Indicate the number of OFDM symbols a UL_RS Zone occupiesNumber of UL region 6 bits Indicates the number of regions defined inUL_RS Zone For (i=0;I<Number of region; i++){ Number of slots } 4 bitsIndicates the number of slots the region includes Number of framesbefore 4 bits Indicates the number of effective frames before theconfiguration takes effect (starting from the current frame) }

The “Type” and “Length” fields indicate the length of the IE and thetype of IE.

The “OFDM symbol index for DL_RS Zone” field indicates an index of theOFDM symbol at which the DL_RS Zone begins. The first “Number of OFDMsymbols” field indicates a number of OFDM symbols which the DL_RS Zoneoccupies. The “Number of DL region” field indicates a number of regionsdefined in the DL_RS Zone. For each DL region the IE also includes a“Number of sub-channels” field that indicates the number of sub-channelsin the DL region. The “OFDM symbol index for UL_RS Zone” field indicatesan index of the OFDM symbol at which the UL_RS Zone begins. The second“Number of OFDM symbols” field indicates a number of OFDM symbols whichthe UL_RS Zone occupies. The “Number of UL region” field indicates anumber of regions defined in UL_RS Zone. For each UL region the IE alsoincludes a “Number of slots” field that indicates the number of slots inthe UL region. The “Number of frames before effective” field indicates anumber of frames before the configuration takes effect, starting fromthe current frame.

The size of each of the fields in Table 5 is indicated in bits. It is tobe understood that the field size is implementation specific and theprovided size is merely for example purposes.

While the RS Zone BRU Configuration IE and the RS Zone RegionConfiguration IE in the examples of Tables 4 and 5 are each presented inthe format of an IE, other formats for providing this information to RSsare considered to be within the scope of the invention described herein.

RS BRU Resource Assignment IE

The RS BRU Resource Assignment IE is used for resource assignment to anRS or multiple RS using a BRU as an RS resource assignment unit. Table 6illustrates an example of a BRU Resource Assignment IE format withparticular field sizes and field contents.

TABLE 6 RS BRU Resource Assignment IE format Syntax Size Notes RS BRUResource Assignment IE { Type 4 bits 0x01 RSID 8 bits Relay station IDNumber of DL BRU 6 bits Indicates the number of DL BRUs assigned to anRS identified by RSID DL MCS 4 bits Indicates the modulation and codingscheme (MCS) to be used in the resource assignment for the RS identifiedby RSID Number UL BRU 6 bits Indicates the number of UL BRUs assigned toan RS identified by RSID UL MCS 4 bits Indicates the MCS to be used inthe resource assignment for the RS identified by RSID }

The “Type” field defines the type of IE. This particular IE has a fixedlength, in the example of Table 6, this is equal to 4 bytes; thereforeno “Length” field is included. The “RSID” field indicates a particulardestination RS the resource assignment is directed to “Number of DL BRU”field and the “Number of UL BRU” field in this IE are respective systemparameters broadcast in the RS Zone BAU Configuration IE. The “DL MCS”and “UL MCS” fields indicate the modulation and coding scheme (MCS) usedfor each of the downlink and uplink resource allocations, respectively.

The size of each of the fields in Table 6 is indicated in bits. It is tobe understood that the field size is implementation specific and theprovided size is merely for example purposes.

While the RS BRU Resource Assignment IE may be useful in particularembodiments, for example when the resource assigned to a given RS is asequential group of DL or UL BRUs of the same number of sub-channels, insome embodiments it may be beneficial to have a resource assignment thatidentifies a particular DL or UL region, for example as defined by theRS Zone Region Configuration IE described above. An example of providingsuch a resource assignment is the Region Resource Assignment IEdescribed below.

RS Region Resource Assignment IE

The Region Resource Assignment IE is used for resource assignment to anRS or multiple RS using a region as an RS resource assignment unit.Table 7 illustrates an example of a Region Resource Assignment IE formatwith particular field sizes and field contents.

TABLE 7 RS Region Resource Assignment IE format Syntax Size Notes RSRegion Resource Assignment IE { Type 4 bits 0x01 RSID 8 bits Relaystation ID DL region ID 6 bits Indicates an identification of a DLregion assigned to an RS identified by RSID DL MCS 4 bits Indicates theMCS to be used in the resource assignment for the RS identified by RSIDUL region ID 6 bits Indicates an identification of an UL region assignedto an RS identified by RSID UL MCS 4 bits Indicates the MCS to be usedin the resource assignment for the RS identified by RSID }

The “Type” field defines the type of IE. This particular IE has a fixedlength, in the example of Table 7, this is equal to 4 bytes, so no“Length” field is included. The “RSID” field indicates a particulardestination RS the resource assignment is directed to “DL region ID”field and “UL region ID” field in this IE are defined in regionconfiguration information provided elsewhere in the R-MAP, for examplein the RS Zone Region Configuration IE described above. The “DL MCS” and“UL MCS” fields indicate the modulation and coding scheme (MCS) used foreach of the down link and up link resource assignments, respectively.

The size of each of the fields in Table 7 is indicated in bits. It is tobe understood that the field size is implementation specific and theprovided size is merely for example purposes.

In some embodiments, the size of the resource assignment IEs are not afixed length. In such a case, a length field may be included in the IE.

TDM Channelization

A first example of DL Resource Multiplexing between BS/RS and RS andbetween BS/RS and MS employs the above-introduced DL RS_Zone for thetransmission from BS/RS to RS. The DL RS_Zone concept is illustrated inFIG. 3. In FIG. 3, a frame 2110 is a two dimensional channel resource inwhich one dimension is represented by logical sub-channels and the otherdimension is represented by OFDM symbols. The frame 2110 includes a DLsub-frame 2120 and a UL sub-frame 2130. In the DL sub-frame 2120 thereis a preamble 2140 and a FCH 2145. A DL_RS Zone 2150 is also included inthe DL sub-frame 2120. This enables the definition of sub-channel typeswith larger resource granularity and therefore less assignment overhead.In some embodiments, the DL_RS Zone 2150 is consistent with the DL_RSZone described above with regard to FIG. 2.

A DL_RS Zone can, for example, be defined to include one or multipleOFDM symbol(s) within a corresponding DL sub-frame or to include anentire DL sub-frame.

Having defined the DL_RS Zone, sub-channelization can be performed toprovide assignment granularity. In some embodiments, a bin conceptsimilar to that used for 802.16e AMC (adaptive modulation and coding)sub-channelization is employed to define a building block forsub-channelization of the DL_RS Zone. A bin is defined as a group ofcontiguous sub-carriers (G) in one OFDM symbol. Sub-carriers in a binindexed as k are re-indexed as sub-carrier(k,i)=sub-carrier Gk+i (i=0,1, . . . , G−1). Each bin includes pilot sub-carriers.

The following is a specific example of how the bin concept can beimplemented, but other examples are possible. For one antenna, asub-carrier indexed with a floor(G/2) is reserved as a pilotsub-carrier. The term “floor” is being used as a mathematical functionfor rounding a real number to a largest integer less than or equal tothe real number. For two antennas, two sub-carriers indexed withfloor(G/2) and floor(G/2)+1 respectively, are reserved as pilotsub-carriers, one pilot sub-carrier for each antenna. For four antennas,four sub-carriers indexed with floor(G/2), floor(G/2)−1, floor(G/2)+1and floor(G/2)+2 respectively, are reserved as pilot sub-carriers, onepilot sub-carrier for each antenna.

Examples of bin construction for even and odd bin sizes for one and twoantennas are provided in FIG. 4. Each of the examples depicts a singlecolumn of rectangular boxes in which the column represents the bin andeach box represents a sub-carrier in the bin. Bin constructions for usein single antenna implementations are illustrated at 2210 and 2220. Abin with G=12 including a pilot in the sixth sub-carrier 2215 isillustrated at 2210. A bin with G=9 including a pilot in the fifthsub-carrier 2225 is illustrated at 2220. Bin constructions for use intwo antenna implementations are illustrated at 2230 and 2240. A bin withG=12 including a pilot for a first antenna in the sixth sub-carrier 2233and a pilot for a second antenna in the seventh antenna 2235 isillustrated at 2230. A bin with G=9 including a pilot for a firstantenna in the fifth sub-carrier 2243 and a pilot for a second antennain the sixth antenna 2245 is illustrated at 2240.

The bins thus defined can then be used to define sub-channels to allowfor DL resource multiplexing. Sub-channelization can be defined by amatrix of N×M bins, in which N is a number of contiguous bins within anOFDM symbol and M as a number of consecutive OFDM symbols. The followingare specific examples of sub-channel types that might be provided: 1×12;1× size of RS Zone (size of RS Zone=number of OFDM symbols of RS Zone);2×6; 2×12; 2× size of RS Zone; 3×6; 3×12; 3× size of RS Zone; 4×6; 4×12;4× size of RS Zone; 6×6; 6×12; 6× size of RS Zone. More generally, thesize of the sub-channel is implementation specific and can be a sizeother than the particular example described above.

FIG. 5 contains examples of two specific sub-channel definitions.Individual bins are identified by a single cross hatched elementindicated at 2330. A sub-channel including multiple bins is identifiedby a thick outline around the multiple bins, as indicated at 2340. A “1×size of RS Zone” type sub-channel is indicated at 2315 in which thesub-channel is a single row of bins equal to the length of the DL_RSZone. A “2×6” type sub-channel is indicated at 2325 in which thesub-channel is a matrix that is two rows of six bins. The DL_RS Zones2310 and 2320 include an implementation specific number of suchsub-channels.

FDM Channelization

In another embodiment, DL Resource Multiplexing between BS/RS and RS andBS/RS and MS is employed on an FDM (frequency division multiplexing)basis. This is particularly applicable in partially used sub-carrier(PUSC) based systems. In a PUSC allocation, full channel diversity isachieved by distributing allocated sub-carriers to sub-channels, wherebythe allocated sub-carriers are a subset of the entire availablebandwidth. For example, in 802.16e, all available sub-carriers used forpilots and data in an OFDM symbol are divided into a set (for examplesix) of major groups and typically two of these major groups areassigned to each sector of a multi-sector transmitter. In anotherembodiment, a respective fractional number of major groups such as theseare dedicated to BS/RS to RS transmission.

In some embodiments, a method employed for sub-channelization is thatwhich is defined in 802.16e, which is hereby incorporated by referencein its entirety. This is a distributed type of channel on the basis ofthe sub-carriers.

In some embodiments, a sub-channel is defined so as to enlargesub-channel size. This is a similar concept to the above-describedbin-based sub-channelization, but in which the bin is replaced by acluster. In some embodiments, clusters of a given sub-channel are notcontiguous. In some embodiments, a cluster is a group of bins. As theclusters of a given sub-channel do not need to be contiguous, adiversity type of sub-channelization is allowable on the basis ofclusters to be defined.

For UL Resource Multiplexing between RS and BS/RS and between MS andBS/RS, the above-introduced UL_RS Zone can be employed, as depicted inFIG. 6 by way of example. In FIG. 6, a frame 2410 is a two dimensionalchannel resource in which one dimension is represented by logicalsub-channels and the other dimension is represented by OFDM symbols. Theframe 2410 includes a DL sub-frame 2420 and a UL sub-frame 2430. In theDL sub-frame 2420 there is a preamble 2440 and a FCH 2445. A UL_RS Zone2450 is also included as a portion of the UL sub-frame 2430. The UL_RSZone is used for the transmission from RS to BS/RS and enables thedefinition of new types of sub-channels. The new types of sub-channelsmay for example reduce the pilot overhead for fixed or low mobile RSand/or allow for larger resource granularity thereby achieving lessassignment overhead. In some embodiments, the UL_RS Zone is consistentwith embodiments described above with regard to FIG. 2.

The UL_RS Zone definition can for example include one or multiple OFDMsymbol(s) within corresponding UL sub-frames, or may include an entireUL sub-frame.

The UL_RS Zone sub-channelization can for example be based on theenhancement of current 802.16e channelization using bin definitions.

A UL bin definition is defined as a group of contiguous sub-carriers (G)in one OFDM symbol. Sub-carriers in a bin indexed as k are re-indexed assub-carrier(k,i)=sub-carrier Gk+i (i=0, 1, . . . , G−1).Bin_without_pilot is defined as a bin where all sub-carriers are usedfor data; Bin_with_pilot is defined to include pilots. In someembodiments, transmissions include sets of bins some of which containpilots and others of which do not to reduce overhead. An example of abin_with_pilot definition for one antenna is a bin where one sub-carrieris indexed with a floor(G/2) reserved as a pilot sub-carrier. An exampleof a bin_with_pilot definition for two antennas is a bin where twosub-carriers are indexed with floor(G/2) and floor(G/2)+1 reserved aspilot sub-carriers. For example, a first antenna transmits a pilot atindex floor(G/2) and a null symbol location at index floor(G/2)+1 and asecond antenna transmits a pilot at index floor(G/2)+1 and a null symbollocation at index floor(G/2). More generally, in some embodiments, afirst bin definition includes pilot symbols, and a second bin definitiondoes not include pilot symbols, and a combination of the two bindefinitions is used for a given sub-channel.

FIG. 7 shows specific examples of bin definitions for two different binsizes and for bins with and without pilots. Each of the examples depictsa single column of rectangular boxes in which the column represents thebin and each box represents a sub-carrier in the bin. A bin for G=8including a pilot in the fourth sub-carrier 2515 is illustrated at 2510.A bin for G=8 without a pilot is illustrated at 2520. A bin for G=9including a pilot in the fifth sub-carrier 2535 is illustrated at 2530.A bin for G=9 without a pilot is illustrated at 2540.

Having defined a bin as a basic unit of channelization, sub-channels canbe defined similar to how it was done for downlink channelization.Specific examples in FIG. 8 illustrate a given type of sub-channel (M,which is a number of OFDM symbols in the sub-channel is known in whichall bins are “bin_without_pilot” bins, except the bins in an OFDM symbolindexed with floor[M/2]. Other breakdowns between bins with pilots andwithout pilots can be employed. In the illustrated example of FIG. 8,individual “bin_without_pilot” bins are identified by a single crosshatched element as indicated at 2630 and “bin_with_pilot” bins areidentified by a single solid black element as indicated by 2640. Asub-channel including multiple bins is identified by a thick outlinearound the multiple bins as indicated by 2650. A “1× size of RS Zone”type sub-channel is indicated at 2615 in which the sub-channel is asingle row of bins equal to the length of the UL_RS Zone. A “2×6” typesub-channel is indicated at 2325 in which the sub-channel is a matrixthat is two rows of six bins. The UL_RS Zones 2610 and 2620 include animplementation specific number of such sub-channels.

In some embodiments, UL Resource Multiplexing between RS and BS/RS andMS and BS/RS is performed using FDM, which is particularly appropriatefor PUSC and/or optional PUSC. In some embodiments, a tile structure asdefined in 802.16e is employed. In some embodiments, a new tilestructure RS_tile is defined. A UL tile can be defined as an N×Mstructure in which N is the number of contiguous sub-carriers within anOFDM symbol and M is the number of OFDM symbols. In this context, a tileis a group of time-frequency resources that includes a band ofsub-carriers being used for signal transmission over a given number ofOFDM symbols. The sub-carriers in the band may be a group of contiguousfrequencies or a logical grouping of non-contiguous frequencies.

In a particular example, an RS_tile type 24×3 (a band of 24 sub-carriersover 3 OFDM symbol durations) is defined. Additional structure typesinclude those having a size of 24×6, 24×12 and 24× size of UL RS_Zone.More generally, the size of the RS_tile is implementation specific andcan be a size other than the particular example described above.

In some embodiments, pilot transmission in a tile is performed with apilot sub-carrier density in RS_tile that is the same as current802.16e. In some embodiments, part of those sub-carriers are used fortransmitting pilots, and part of those sub-carriers are used forsounding. A specific example of this is shown in FIG. 9. Pilot pattern2710 is an example of a UL OPUSC pilot pattern having a basic tilestructure including pilot sub-carriers (indicated by 2740 in legend2730) in a first row of 3 sub-carrier by 3 OFDM symbol tiles andsub-carriers used for sounding (indicated by 2750 in legend 2730) in asecond row of 3 sub-carrier by 3 OFDM symbol tiles. In otherembodiments, a pilot density lower than that of the current 802.16e tileis employed. Pilot pattern 2720 is an example of a UL OPUSC pilotpattern having a similar tile structure to 2710 including pilotsub-carriers in a first row of 3 sub-carrier by 3 OFDM symbol tiles andno pilot sub-carriers.

In another embodiment, the entire frame resource is initially assumed tobe available for use for RS related transmission (DL/UL). RSsub-channels (RS_sub-channel) can be defined using any appropriatemethod including but not limited to those described above. In someembodiments, the resource used for MSs is assigned first using 802.16esub-channels and RS related resources are assigned later using RSsub-channels. All resources occupied by MSs will be punctured out, orremoved from the sub-channels to allow for the assigned resource for RS.This avoids hard partitioning between RS related resource and MS relatedresource.

Description of Example Components of a Relay System

For the purpose of providing context for embodiments of the inventionfor use in a communication system, FIG. 10 shows a base stationcontroller (BSC) 10 which controls wireless communications withinmultiple cells 12, which cells are served by corresponding base stations(BS) 14. In general, each base station 14 facilitates communicationsusing OFDM with mobile and/or wireless terminals 16, which are withinthe cell 12 associated with the corresponding base station 14. Themovement of the mobile terminals 16 in relation to the base stations 14results in significant fluctuation in channel conditions. Asillustrated, the base stations 14 and mobile terminals 16 may includemultiple antennas to provide spatial diversity for communications. Alsoshown are relay stations 17.

A high level overview of the mobile terminals 16 and base stations 14upon which aspects of the present invention are implemented is providedprior to delving into the structural and functional details of thepreferred embodiments. With reference to FIG. 11, a base station 14 isillustrated. The base station 14 generally includes a control system 20,a baseband processor 22, transmit circuitry 24, receive circuitry 26,multiple antennas 28, and a network interface 30. The receive circuitry26 receives radio frequency signals bearing information from one or moreremote transmitters provided by mobile terminals 16 (illustrated in FIG.10). A low noise amplifier and a filter (not shown) may co-operate toamplify and remove broadband interference from the signal forprocessing. Downconversion and digitization circuitry (not shown) willthen downconvert the filtered, received signal to an intermediate orbaseband frequency signal, which is then digitized into one or moredigital streams.

The baseband processor 22 processes the digitized received signal toextract the information or data bits conveyed in the received signal.This processing typically comprises demodulation, decoding, and errorcorrection operations. As such, the baseband processor 22 is generallyimplemented in one or more digital signal processors (DSPs) orapplication-specific integrated circuits (ASICs). The receivedinformation is then sent across a wireless network via the networkinterface 30 or transmitted to another mobile terminal 16 serviced bythe base station 14.

On the transmit side, the baseband processor 22 receives digitized data,which may represent voice, data, or control information, from thenetwork interface 30 under the control of control system 20, and encodesthe data for transmission. The encoded data is output to the transmitcircuitry 24, where it is modulated by a carrier signal having a desiredtransmit frequency or frequencies. A power amplifier (not shown) willamplify the modulated carrier signal to a level appropriate fortransmission, and deliver the modulated carrier signal to the antennas28 through a matching network (not shown). Various modulation andprocessing techniques available to those skilled in the art are used forsignal transmission between the base station and the mobile terminal.

With reference to FIG. 12, a mobile terminal 16 configured according toone embodiment of the present invention is illustrated. Similarly to thebase station 14, the mobile terminal 16 will include a control system32, a baseband processor 34, transmit circuitry 36, receive circuitry38, multiple antennas 40, and user interface circuitry 42. The receivecircuitry 38 receives radio frequency signals bearing information fromone or more base stations 14. A low noise amplifier and a filter (notshown) may co-operate to amplify and remove broadband interference fromthe signal for processing. Downconversion and digitization circuitry(not shown) will then downconvert the filtered, received signal to anintermediate or baseband frequency signal, which is then digitized intoone or more digital streams.

The baseband processor 34 processes the digitized received signal toextract the information or data bits conveyed in the received signal.This processing typically comprises demodulation, decoding, and errorcorrection operations. The baseband processor 34 is generallyimplemented in one or more digital signal processors (DSPs) andapplication specific integrated circuits (ASICs).

For transmission, the baseband processor 34 receives digitized data,which may represent voice, data, or control information, from thecontrol system 32, which it encodes for transmission. The encoded datais output to the transmit circuitry 36, where it is used by a modulatorto modulate a carrier signal that is at a desired transmit frequency orfrequencies. A power amplifier (not shown) will amplify the modulatedcarrier signal to a level appropriate for transmission, and deliver themodulated carrier signal to the antennas 40 through a matching network(not shown). Various modulation and processing techniques available tothose skilled in the art are used for signal transmission between themobile terminal and the base station.

In OFDM modulation, the transmission band is divided into multiple,orthogonal carrier waves. Each carrier wave is modulated according tothe digital data to be transmitted. Because OFDM divides thetransmission band into multiple carriers, the bandwidth per carrierdecreases and the modulation time per carrier increases. Since themultiple carriers are transmitted in parallel, the transmission rate forthe digital data, or symbols, on any given carrier is lower than when asingle carrier is used.

OFDM modulation utilizes the performance of an Inverse Fast FourierTransform (IFFT) on the information to be transmitted. For demodulation,the performance of a Fast Fourier Transform (FFT) on the received signalrecovers the transmitted information. In practice, the IFFT and FFT areprovided by digital signal processing carrying out an Inverse DiscreteFourier Transform (IDFT) and Discrete Fourier Transform (DFT),respectively. Accordingly, the characterizing feature of OFDM modulationis that orthogonal carrier waves are generated for multiple bands withina transmission channel. The modulated signals are digital signals havinga relatively low transmission rate and capable of staying within theirrespective bands. The individual carrier waves are not modulateddirectly by the digital signals. Instead, all carrier waves aremodulated at once by IFFT processing.

In operation, OFDM is preferably used for at least down-linktransmission from the base stations 14 to the mobile terminals 16. Eachbase station 14 is equipped with “n” transmit antennas 28, and eachmobile terminal 16 is equipped with “m” receive antennas 40. Notably,the respective antennas can be used for reception and transmission usingappropriate duplexers or switches and are so labelled only for clarity.

With reference to FIG. 13, a logical OFDM transmission architecture willbe described. Initially, the base station controller 10 will send datato be transmitted to various mobile terminals 16 to the base station 14.The base station 14 may use the channel quality indicators (CQIs)associated with the mobile terminals to schedule the data fortransmission as well as select appropriate coding and modulation fortransmitting the scheduled data. The CQIs may be directly from themobile terminals 16 or determined at the base station 14 based oninformation provided by the mobile terminals 16. In either case, the CQIfor each mobile terminal 16 is a function of the degree to which thechannel amplitude (or response) varies across the OFDM frequency band.

Scheduled data 44, which is a stream of bits, is scrambled in a mannerreducing the peak-to-average power ratio associated with the data usingdata scrambling logic 46. A cyclic redundancy check (CRC) for thescrambled data is determined and appended to the scrambled data usingCRC adding logic 48. Next, channel coding is performed using channelencoder logic 50 to effectively add redundancy to the data to facilitaterecovery and error correction at the mobile terminal 16. Again, thechannel coding for a particular mobile terminal 16 is based on the CQI.In some implementations, the channel encoder logic 50 uses known Turboencoding techniques. The encoded data is then processed by rate matchinglogic 52 to compensate for the data expansion associated with encoding.

Bit interleaver logic 54 systematically reorders the bits in the encodeddata to minimize the loss of consecutive data bits. The resultant databits are systematically mapped into corresponding symbols depending onthe chosen baseband modulation by mapping logic 56. Preferably,Quadrature Amplitude Modulation (QAM) or Quadrature Phase Shift Key(QPSK) modulation is used. The degree of modulation is preferably chosenbased on the CQI for the particular mobile terminal. The symbols may besystematically reordered to further bolster the immunity of thetransmitted signal to periodic data loss caused by frequency selectivefading using symbol interleaver logic 58.

At this point, groups of bits have been mapped into symbols representinglocations in an amplitude and phase constellation. When spatialdiversity is desired, blocks of symbols are then processed by space-timeblock code (STC) encoder logic 60, which modifies the symbols in afashion making the transmitted signals more resistant to interferenceand more readily decoded at a mobile terminal 16. The STC encoder logic60 will process the incoming symbols and provide “n” outputscorresponding to the number of transmit antennas 28 for the base station14. The control system 20 and/or baseband processor 22 as describedabove with respect to FIG. 11 will provide a mapping control signal tocontrol STC encoding. At this point, assume the symbols for the “n”outputs are representative of the data to be transmitted and capable ofbeing recovered by the mobile terminal 16.

For the present example, assume the base station 14 has two antennas 28(n=2) and the STC encoder logic 60 provides two output streams ofsymbols. Accordingly, each of the symbol streams output by the STCencoder logic 60 is sent to a corresponding IFFT processor 62,illustrated separately for ease of understanding. Those skilled in theart will recognize that one or more processors may be used to providesuch digital signal processing, alone or in combination with otherprocessing described herein. The IFFT processors 62 will preferablyoperate on the respective symbols to provide an inverse FourierTransform. The output of the IFFT processors 62 provides symbols in thetime domain. The time domain symbols are grouped into frames, which areassociated with a prefix by prefix insertion logic 64. Each of theresultant signals is up-converted in the digital domain to anintermediate frequency and converted to an analog signal via thecorresponding digital up-conversion (DUO) and digital-to-analog (D/A)conversion circuitry 66. The resultant (analog) signals are thensimultaneously modulated at the desired RF frequency, amplified, andtransmitted via the RF circuitry 68 and antennas 28. Notably, pilotsignals known by the intended mobile terminal 16 are scattered among thesub-carriers. The mobile terminal 16, which is discussed in detailbelow, will use the pilot signals for channel estimation.

Reference is now made to FIG. 14 to illustrate reception of thetransmitted signals by a mobile terminal 16. Upon arrival of thetransmitted signals at each of the antennas 40 of the mobile terminal16, the respective signals are demodulated and amplified bycorresponding RF circuitry 70. For the sake of conciseness and clarity,only one of the two receive paths is described and illustrated indetail. Analog-to-digital (A/D) converter and down-conversion circuitry72 digitizes and downconverts the analog signal for digital processing.The resultant digitized signal may be used by automatic gain controlcircuitry (AGO) 74 to control the gain of the amplifiers in the RFcircuitry 70 based on the received signal level.

Initially, the digitized signal is provided to synchronization logic 76,which includes coarse synchronization logic 78, which buffers severalOFDM symbols and calculates an auto-correlation between the twosuccessive OFDM symbols. A resultant time index corresponding to themaximum of the correlation result determines a fine synchronizationsearch window, which is used by fine synchronization logic 80 todetermine a precise framing starting position based on the headers. Theoutput of the fine synchronization logic 80 facilitates frameacquisition by frame alignment logic 84. Proper framing alignment isimportant so that subsequent FFT processing provides an accurateconversion from the time domain to the frequency domain. The finesynchronization algorithm is based on the correlation between thereceived pilot signals carried by the headers and a local copy of theknown pilot data. Once frame alignment acquisition occurs, the prefix ofthe OFDM symbol is removed with prefix removal logic 86 and resultantsamples are sent to frequency offset correction logic 88, whichcompensates for the system frequency offset caused by the unmatchedlocal oscillators in the transmitter and the receiver. Preferably, thesynchronization logic 76 includes frequency offset and clock estimationlogic 82, which is based on the headers to help estimate such effects onthe transmitted signal and provide those estimations to the correctionlogic 88 to properly process OFDM symbols.

At this point, the OFDM symbols in the time domain are ready forconversion to the frequency domain using FFT processing logic 90. Theresults are frequency domain symbols, which are sent to processing logic92. The processing logic 92 extracts the scattered pilot signal usingscattered pilot extraction logic 94, determines a channel estimate basedon the extracted pilot signal using channel estimation logic 96, andprovides channel responses for all sub-carriers using channelreconstruction logic 98. In order to determine a channel response foreach of the sub-carriers, the pilot signal is essentially multiple pilotsymbols that are scattered among the data symbols throughout the OFDMsub-carriers in a known pattern in both time and frequency. Examples ofscattering of pilot symbols among available sub-carriers over a giventime and frequency plot in an OFDM environment are found in PCT PatentApplication No. PCT/CA2005/000387 filed Mar. 15, 2005 assigned to thesame assignee of the present application. Continuing with FIG. 14, theprocessing logic compares the received pilot symbols with the pilotsymbols that are expected in certain sub-carriers at certain times todetermine a channel response for the sub-carriers in which pilot symbolswere transmitted. The results are interpolated to estimate a channelresponse for most, if not all, of the remaining sub-carriers for whichpilot symbols were not provided. The actual and interpolated channelresponses are used to estimate an overall channel response, whichincludes the channel responses for most, if not all, of the sub-carriersin the OFDM channel.

The frequency domain symbols and channel reconstruction information,which are derived from the channel responses for each receive path areprovided to an STC decoder 100, which provides STC decoding on bothreceived paths to recover the transmitted symbols. The channelreconstruction information provides equalization information to the STCdecoder 100 sufficient to remove the effects of the transmission channelwhen processing the respective frequency domain symbols

The recovered symbols are placed back in order using symbolde-interleaver logic 102, which corresponds to the symbolinterleave/logic 58 of the transmitter. The de-interleaved symbols arethen demodulated or de-mapped to a corresponding bitstream usingde-mapping logic 104. The bits are then de-interleaved using bitde-interleaver logic 106, which corresponds to the bit interleaver logic54 of the transmitter architecture. The de-interleaved bits are thenprocessed by rate de-matching logic 108 and presented to channel decoderlogic 110 to recover the initially scrambled data and the CRC checksum.Accordingly, CRC logic 112 removes the CRC checksum, checks thescrambled data in traditional fashion, and provides it to thede-scrambling logic 114 for de-scrambling using the known base stationde-scrambling code to recover the originally transmitted data 116.

In parallel to recovering the data 116, a CQI, or at least informationsufficient to create a CQI at the base station 14, is determined andtransmitted to the base station 14. As noted above, the CQI may be afunction of the carrier-to-interference ratio (CR), as well as thedegree to which the channel response varies across the varioussub-carriers in the OFDM frequency band. The channel gain for eachsub-carrier in the OFDM frequency band being used to transmitinformation is compared relative to one another to determine the degreeto which the channel gain varies across the OFDM frequency band.Although numerous techniques are available to measure the degree ofvariation, one technique is to calculate the standard deviation of thechannel gain for each sub-carrier throughout the OFDM frequency bandbeing used to transmit data.

FIGS. 10 to 14 each provide a specific example of a communication systemor elements of a communication system that could be used to implementembodiments of the invention. It is to be understood that embodiments ofthe invention can be implemented with communications systems havingarchitectures that are different than the specific example, but thatoperate in a manner consistent with the implementation of theembodiments as described herein.

For multi-hop implementations such as described previously, each relaynode will include some transmitting functionality and some receivingfunctionality. For example, a relay station may include components ofthe example OFDM transmitter architecture and the example OFDM receiverarchitecture.

Numerous modifications and variations of the present invention arepossible in light of the above teachings. It is therefore to beunderstood that within the scope of the appended claims, the inventionmay be practised otherwise than as specifically described herein.

The invention claimed is:
 1. A method for use in an orthogonal frequencydivision multiplexed (OFDM) communication system employing relaystations (RSs) comprising: assigning a distinct pseudo-random noise (PN)sequence to each base station (BS) and each RS; storing, in each RS, thedistinct PN sequence for the respective RS; generating, by each RS, apreamble based on the distinct PN sequence for the respective RS; andtransmitting by each RS, a signal to at least one mobile station (MS),the signal including the preamble corresponding to the respective RS. 2.The method of claim 1, further comprising, for purposes of routing,identifying each BS or RS by a BS identification in one of themanagement messages.
 3. The method of claim 2, wherein identifying eachRS comprises assigning each RS a base station identifier in themanagement message.
 4. The method of claim 1, wherein assigning adistinct PN sequence for a mobile relay station (MRS) is staticallydefined even when there is a handoff.
 5. The method of claim 4, furthercomprising defining for MRSs a system reserved PN index so as to avoidcollisions when a MS moves across the OFDM communication system.
 6. Themethod of claim 4, wherein the PN index is re-assigned during when a MSmoves across the OFDM communication system and further comprisinginforming any attached MSs of the change and/or performingre-synchronization.
 7. The method of claim 1, further comprising:modifying a management message to include the distinct PN sequence; andidentifying one of the respective RSs based on the management message.8. A relay station configured to communicate via an orthogonal frequencydivision multiplexed (OFDM) communication system, comprising: a memory;and a processor configured to: use one pseudo-random noise (PN) sequencefrom a plurality of PN sequences, wherein the one PN sequence isdistinct from PN sequences assigned to other relay stations and basestations in a communication area of the relay station; store thedistinct PN sequence for the relay station in the memory generate apreamble based on the distinct PN sequence for the relay station; andtransmit a signal to at least one mobile station (MS), the signalincluding the preamble.
 9. The relay station of claim 8, wherein theprocessor is further configured to, for purposes of routing; identifyeach BS or RS by a BS identification in one of the management messages.10. The relay station of claim 9, wherein identifying each RS comprisesassigning each RS a base station identifier in the management message.11. The relay station of claim 8, wherein assigning a distinct PNsequence for a mobile relay station (MRS) is statically defined evenwhen there is a handoff.
 12. The relay station of claim 11, wherein theprocessor is further configured to; define, for MRSs, a system reservedPN index so as to avoid collisions when a MS moves across the OFDMcommunication system.
 13. The relay station of claim 11, wherein the PNindex is re-assigned during when a MS moves across the OFDMcommunication system and wherein the processor is further configured to;inform any attached MSs of the change and/or performingre-synchronization.
 14. The relay station of claim 8, wherein theprocessor is further configured to; modify a management message toinclude the distinct PN sequence; and identify one of the respective RSsbased on the management message.
 15. A non-transitory computer readablestorage medium with an executable program stored thereon that isexecutable by a processor, the computer readable storage medium andprocessor being configured to communicate via an orthogonal frequencydivision multiplexed (OFDM) communication system, wherein the programinstructs the processor to: use one pseudo-random noise (PN) sequencefrom a plurality of PN sequences, wherein the one PN sequence isdistinct from PN sequences assigned to relay stations and base stationsin a communication area of the processor; store the distinct PN sequencefor the processor in the memory generate a preamble based on thedistinct PN sequence for the processor; and transmit a signal to atleast one mobile station (MS), the signal including the preamble. 16.The non-transitory computer readable storage medium of claim 15, whereinthe processor is further configured to, for purposes of routing;identify each BS or RS by a BS identification in one of the managementmessages.
 17. The non-transitory computer readable storage medium ofclaim 16, wherein identifying each RS comprises assigning each RS a basestation identifier in the management message.
 18. The non-transitorycomputer readable storage medium of claim 15, wherein assigning adistinct PN sequence for a mobile relay station (MRS) is staticallydefined even when there is a handoff.
 19. The non-transitory computerreadable storage medium of claim 18, wherein the processor is furtherconfigured to; define, for MRSs, a system reserved PN index so as toavoid collisions when a MS moves across the OFDM communication system.20. The non-transitory computer readable storage medium of claim 15,wherein the processor is further configured to; modify a managementmessage to include the distinct PN sequence; and identify one of therespective RSs based on the management message.